Abstract(#br)Early assessment of response to neoadjuvant chemotherapy (NAC) might be helpful in avoiding the toxicity of ineffective chemotherapy and allowing refinement of treatment. We conducted a review of the literature regarding the applicability of 18F-FDG PET/CT to the prediction of an early pathological response in different subgroups of breast cancer. Clinical research in this field has intensified in the last few years. Early studies by various groups have shown the potential of 18F-FDG PET/CT in the early assessment of response to NAC. However, interim PET/CT in breast cancer has not yet gained wide acceptance compared to its use in other settings such as lymphomas. This is in part due to a lack of consensus that early evaluation of response can be used to... direct change in therapy in the neoadjuvant breast cancer setting, and only limited data showing that response-adaptive therapy leads to improved outcomes. However, one major element that has hampered the use of 18F-FDG PET/CT in directing neoadjuvant therapy is its evaluation in populations with mixed subtypes of breast cancer. However, major improvements have occurred in recent years. Pilot studies have highlighted the need for considering breast cancer subtype and the type of treatment, and have offered criteria for the use of PET/CT for the early prediction of response in specific settings. 18F-FDG PET/CT has considerable potential for the early prediction of pathological complete response to NAC in aggressive subtypes such as triple-negative or HER2-positive breast cancers. The results of a multicentre trial that used early metabolic response on 18F-FDG PET/CT as a means to select poor responders to adapt neoadjuvant treatment have recently been published. Other trials are ongoing or being planned.